## Local Structures > [!definition|*] V-Structures and Colliders > Vertex triplets $(i,~j,~k)$ where $i\to k\leftarrow j$ but $i\not \sim j$ is called a **v-structure**: > ```mermaid > graph LR > i --> k > k ~~~ j --> k > j ~~~ k > ``` > The center $k$ of the v-structure is called a **collider**. ^d17b82 - Here $a \to b$ means that the edge $\vec{ab}$ exists, not that there exists a path going from $a$ to $b$.